The invention relates to a method for the magnetic recording of encoded digital information signals on a magnetic recording medium with the assistance of a magnetic head to which a write current is supplied. As a function of the information signals, the head executes a change from a first current value to a second current value and vice versa. The invention also relates to a device for the implementation of the method.
The magnetic recording of encoded digital information signals on a magnetic recording medium, for example, on a magnetic tape, with the assistance of a magnetic head has been known for a long time. For this purpose, a write current is supplied to the magnetic head which, in accordance with the encoded digital information signals, carries out a change between a first current value and a second current value and vice versa corresponding to the employed encoding method. Accordingly, the current values are selected in such manner that the magnetic recording medium is brought to saturation. The number of changes between the current values (which is known as a "head change" in the following text) per digital information signal depends upon the employed encoding method. Such encoding methods derive, for example, from the U.S. Pat. No. 4,167,761, incorporated herein by reference. A circuit arrangement which generates a write current for a magnetic head is also disclosed in the aforementioned patent.
The magnetic recording medium, for example, a magnetic tape, is thus brought into one of two possible saturation states depending upon the employed encoding method, namely it is magnetized in one of two longitudinal directions. Accordingly, in all possible encoding methods, a problem exists that, given a change of the frequency of the head change and corresponding to the flux change on the magnetic recording medium, a low frequency component arises, namely in the areas in which a transition is made on the recording medium from low recording density (little flux change) to high recording density (great flux change) and vice versa. The result of these low frequency components is that the high frequency read signals picked up from the magnetic recording medium are shifted relative to a base line. The maximum amplitude of these low frequency components exists in the transition areas in which the frequency changes occur and prevents a correct information recognition.
The reason for this phenomenon is as follows: when the information signal is recorded in the recording medium, the remanent magnetization is a function of the wavelength and is lower for high recording densities. Independently of the mutual influence between the particles in the recording medium, the area with high remanent magnetization expands into the area with lower magnetization. This results in the fact that the magnetization pattern on the recording medium is distorted and this distortion appears as a low frequency component. This low frequency component affects the read signal to such an extent that the high frequency read signals are shifted in their position in the transition areas from lower to higher and higher to lower frequency in comparison to undistorted read signals.
In order to reduce the influence of such distortions, it is known to appropriately pre-emphasize or pre-distort the write current. As an example, see U.S. Pat. No. 4,167,761, German Auslegeschrift No. 21 11 744, and German Offenlegungsschrift No. 17 47 004, all incorporated herein by reference. Whenever, in accordance with the encoding method, a flux change is to be carried out on the magnetic recording medium, the write current for the magnetic head there is switched from a first current value to a second current value, i.e. a head change is undertaken and subsequently the write current is changed either in one step or continuously from the current value to a value lower in amplitude. This form of the write current and the magnetization of the recording medium corresponding to this form reduces the distortion of the read signals.